U.S. patent application number 13/790295 was filed with the patent office on 2013-12-12 for color time domain integration camera having a single charge coupled device and fringe projection auto-focus system.
This patent application is currently assigned to NIKON CORPORATION. The applicant listed for this patent is NIKON CORPORATION. Invention is credited to Eric Peter Goodwin.
Application Number | 20130330662 13/790295 |
Document ID | / |
Family ID | 49715544 |
Filed Date | 2013-12-12 |
United States Patent
Application |
20130330662 |
Kind Code |
A1 |
Goodwin; Eric Peter |
December 12, 2013 |
COLOR TIME DOMAIN INTEGRATION CAMERA HAVING A SINGLE CHARGE COUPLED
DEVICE AND FRINGE PROJECTION AUTO-FOCUS SYSTEM
Abstract
A detector (550) for detecting light (248B) from a light source
(248A) comprises a single array of pixels (574) and a first mask
(576). The single array of pixels (574) includes a plurality of
rows of pixels (574R), and a plurality of columns of pixels (574C)
having at least a first active column of pixels (574AC) and a
spaced apart second active column of pixels (574AC). The first mask
(576) covers one of the plurality of columns of pixels (574C) to
provide a first masked column of pixels (574MC) that is positioned
between the first active column of pixels (574AC) and the second
active column of pixels (574AC). Additionally, a charge is
generated from the light (248B) impinging on the first active
column of pixels (574AC), is transferred to the first masked column
of pixels (574MC), and subsequently is transferred to the second
active column of pixels (574AC).
Inventors: |
Goodwin; Eric Peter;
(Tucson, AZ) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NIKON CORPORATION |
Tokyo |
|
JP |
|
|
Assignee: |
NIKON CORPORATION
Tokyo
JP
|
Family ID: |
49715544 |
Appl. No.: |
13/790295 |
Filed: |
March 8, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61658819 |
Jun 12, 2012 |
|
|
|
61674766 |
Jul 23, 2012 |
|
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Current U.S.
Class: |
430/30 ; 250/216;
250/578.1; 356/364; 356/614 |
Current CPC
Class: |
G03F 9/7026 20130101;
G03F 7/70 20130101; G02B 7/36 20130101; G01B 11/25 20130101; G01B
11/14 20130101; G01J 1/42 20130101; G03F 7/70725 20130101; G03F
7/70775 20130101 |
Class at
Publication: |
430/30 ; 250/216;
356/614; 356/364; 250/578.1 |
International
Class: |
G01J 1/42 20060101
G01J001/42; G01B 11/14 20060101 G01B011/14 |
Claims
1. A detector for detecting light from a light source, the detector
comprising: a single array of pixels including (i) a plurality of
rows of pixels and (ii) a plurality of columns of pixels having at
least a first active column of pixels and a spaced apart second
active column of pixels; and a first mask that covers one of the
plurality of columns of pixels to provide a first masked column of
pixels that is positioned between the first active column of pixels
and the second active column of pixels; wherein a charge is
generated from the light impinging on the first active column of
pixels, is transferred to the first masked column of pixels, and
subsequently is transferred to the second active column of
pixels.
2. The detector of claim 1 wherein an accumulation of the charge
from the light impinging on the first active column of pixels and
the second active column of pixels generates an output charge.
3. The detector of claim 1 wherein no active column of pixels is
positioned adjacent to another active column of pixels.
4. The detector of claim 1 wherein the plurality of columns of
pixels further includes a third active column of pixels that is
spaced apart from the first active column of pixels and the second
active column of pixels, and further comprising a second mask that
covers one of the plurality of columns of pixels to provide a
second masked column of pixels that is positioned between the
second active column of pixels and the third active column of
pixels.
5. The detector of claim 4 wherein the plurality of columns of
pixels further includes a fourth active column of pixels that is
spaced apart from the first active column of pixels, the second
active column of pixels, and the third active column of pixels, and
further comprising a third mask that covers one of the plurality of
columns of pixels to provide a third masked column of pixels that
is positioned between the third active column of pixels and the
fourth active column of pixels.
6. The detector of claim 1 further comprising a second mask that
covers one of the plurality of columns of pixels to provide a
second masked column of pixels that is positioned between the first
active column of pixels and the second active column of pixels.
7. The detector of claim 6 further comprising a third mask that
covers one of the plurality of columns of pixels to provide a third
masked column of pixels that is positioned between the first active
column of pixels and the second active column of pixels.
8. The detector of claim 1 further comprising a lenslet array that
is positioned substantially adjacent to a top surface of the
detector.
9. The detector of claim 1 wherein the first active column of
pixels and the second active column are arranged along a first
direction, and are spaced apart from one another along a second
direction that crosses the first direction.
10. The detector of claim 9 wherein the first mask is positioned
between the first active column of pixels and the second active
column of pixels in relation to the second direction.
11. A position system for measuring the position of a work piece,
the position system comprising a light source that generates (i) a
first light beam that is directed at the work piece at a first
time, the first light beam having a first characteristic, and (ii)
a second light beam that is directed at the work piece at a second
time, the second light beam having a second characteristic that is
different than the first characteristic; and the detector of claim
1 that detects the first light beam and the second light beam from
the light source.
12. The position system of claim 11 wherein the first
characteristic is a first wavelength range and the second
characteristic is a second wavelength range that is different than
the first wavelength range.
13. The position system of claim 11 wherein the first
characteristic is a first polarization and the second
characteristic is a second polarization that is different than the
first polarization.
14. The position system of claim 11 wherein the first
characteristic includes the first light beam being a measurement
beam, and wherein the second characteristic includes the second
light beam being a reference beam.
15. The position system of claim 11 wherein the detector further
comprises a second mask that covers one of the plurality of columns
of pixels to provide a second masked column of pixels that is
positioned between the first active column of pixels and the second
active column of pixels; wherein the light source further generates
a third light beam that is directed at the work piece at a third
time, the third light beam having a third characteristic that is
different than at least one of the first characteristic and the
second characteristic; and wherein the detector detects the first
light beam, the second light beam and the third light beam from the
light source.
16. The position system of claim 15 wherein the detector further
comprises a third mask that covers one of the plurality of columns
of pixels to provide a third masked column of pixels that is
positioned between the first active column of pixels and the second
active column of pixels; wherein the light source further generates
a fourth light beam that is directed at the work piece at a fourth
time, the fourth light beam having a fourth characteristic that is
different than at least one of the first characteristic, the second
characteristic and the third characteristic; and wherein the
detector detects the first light beam, the second light beam, the
third light beam and the fourth light beam from the light
source.
17. An exposure apparatus including a stage assembly that positions
a work piece, and the position system of claim 11 that measures the
position of the workpiece.
18. A process for manufacturing a wafer that includes the steps of
providing a substrate, and transferring a mask pattern to the
substrate with the exposure apparatus of claim 17.
19. A method for detecting light from a light source, the method
comprising the steps of: providing a single array of pixels
including (i) a plurality of rows of pixels and (ii) a plurality of
columns of pixels having at least a first active column of pixels
and a spaced apart second active column of pixels; covering one of
the plurality of columns of pixels with a first mask to provide a
first masked column of pixels that is positioned between the first
active column of pixels and the second active column of pixels;
generating a charge from the light impinging on the first active
column of pixels; transferring the charge from the first active
column of pixels to the first masked column of pixels; and
subsequently transferring the charge to the second active column of
pixels.
20. The method of claim 19 further comprising the step of
generating an output charge from an accumulation of the charge from
the light impinging on the first active column of pixels and the
second active column of pixels.
21. The method of claim 19 wherein the step of providing includes
no active column of pixels being positioned adjacent to another
active column of pixels.
22. The method of claim 19 wherein the step of providing includes
the plurality of columns of pixels further including a third active
column of pixels that is spaced apart from the first active column
of pixels and the second active column of pixels, and further
comprising the step of covering one of the plurality of columns of
pixels with a second mask to provide a second masked column of
pixels that is positioned between the second active column of
pixels and the third active column of pixels.
23. The method of claim 22 wherein the step of providing includes
the plurality of columns of pixels further including a fourth
active column of pixels that is spaced apart from the first active
column of pixels, the second active column of pixels, and the third
active column of pixels, and further comprising the step of
covering one of the plurality of columns of pixels with a third
mask to provide a third masked column of pixels that is positioned
between the third active column of pixels and the fourth active
column of pixels.
24. The method of claim 19 further comprising the step of covering
one of the plurality of columns of pixels with a second mask to
provide a second masked column of pixels that is positioned between
the first active column of pixels and the second active column of
pixels.
25. The method of claim 24 further comprising the step of covering
one of the plurality of columns of pixels with a third mask to
provide a third masked column of pixels that is positioned between
the first active column of pixels and the second active column of
pixels.
26. The method of claim 19 further comprising the step of
positioning a lenslet array substantially adjacent to a top surface
of the single array of pixels.
27. The method of claim 1 wherein the first active column of pixels
and the second active column are arranged along a first direction,
and are spaced apart along a second direction that is orthogonal to
the first direction.
28. The method of claim 27 wherein the first mask is positioned
between the first active column of pixels and the second active
column of pixels in relation to the second direction.
29. A method for measuring the position of a work piece, the method
comprising the steps of: generating a first light beam with a light
source, the first light beam having a first characteristic;
directing the first light beam at the work piece at a first time,
the work piece reflecting the first light beam; generating a second
light beam with the light source, the second light beam having a
second characteristic that is different than the first
characteristic; directing the second light beam at the work piece
at a second time, the work piece reflecting the second light beam;
and detecting the first light beam and the second light beam that
are reflected off of the work piece with the method of claim
19.
30. The method of claim 29 wherein the step of generating the first
light beam includes the first characteristic being a first
wavelength range, and wherein the step of generating the second
light beam includes the second characteristic being a second
wavelength range that is different than the first wavelength
range.
31. The method of claim 29 wherein the step of generating the first
light beam includes the first characteristic being a first
polarization, and wherein the step of generating the second light
beam includes the second characteristic being a second polarization
that is different than the first polarization.
32. The method of claim 29 further comprising the steps of (i)
covering one of the plurality of columns of pixels with a second
mask to provide a second masked column of pixels that is positioned
between the first active column of pixels and the second active
column of pixels; (ii) generating a third light beam with the light
source, the third light beam having a third characteristic that is
different than at least one of the first characteristic and the
second characteristic; and (iii) directing the third light beam at
the work piece at a third time, the work piece reflecting the third
light beam; and wherein the step of detecting includes detecting
the first light beam, the second light beam and the third light
beam that are reflected off of the work piece.
33. The method of claim 32 further comprising the steps of (i)
covering one of the plurality of columns of pixels with a third
mask to provide a third masked column of pixels that is positioned
between the first active column of pixels and the second active
column of pixels; (ii) generating a fourth light beam with the
light source, the fourth light beam having a fourth characteristic
that is different than at least one of the first characteristic,
the second characteristic and the third characteristic; and (iii)
directing the fourth light beam at the work piece at a fourth time,
the work piece reflecting the fourth light beam; and wherein the
step of detecting includes detecting the first light beam, the
second light beam, the third light beam and the fourth light beam
that are reflected off of the work piece.
34. A method for exposing a work piece, the method comprising the
steps of positioning the work piece with a stage assembly, and
measuring the position of the work piece with the method of claim
29.
Description
RELATED INVENTION
[0001] The application claims priority on U.S. Provisional
Application Ser. Nos. 61/658,819 filed on Jun. 12, 2012, entitled
"COLOR TIME DOMAIN INTEGRATION CAMERA HAVING A SINGLE CHARGE
COUPLED DEVICE AND FRINGE PROJECTION AUTO-FOCUS SYSTEM", and
61/674,766 filed on Jul. 23, 2012, entitled "COLOR TIME DOMAIN
INTEGRATION CAMERA HAVING A SINGLE CHARGE COUPLED DEVICE AND FRINGE
PROJECTION AUTO-FOCUS SYSTEM". As far as is permitted, the contents
of U.S. Provisional Application Ser. Nos. 61/658,819 and 61/674,766
are incorporated herein by reference.
BACKGROUND
[0002] Exposure apparatuses are commonly used to transfer images
from a reticle onto a semiconductor wafer during semiconductor
processing. A typical exposure apparatus includes an illumination
source, a reticle stage assembly that positions a reticle, an
optical assembly having an optical axis, a wafer stage assembly
that positions a semiconductor wafer, a measurement (or position)
system, and a control system. The measurement system constantly
monitors the position of the reticle and the wafer, and the control
system controls each stage assembly to constantly adjust the
position of the reticle and the wafer. The features of the images
transferred from the reticle onto the wafer are extremely small.
Accordingly, the precise positioning of the wafer and the reticle
is critical to the manufacturing of high quality wafers.
[0003] There is a constant desire to improve the accuracy of the
measurement system. In certain designs, the measurement system
includes an autofocus system that is used to map the topography of
the wafer surface along the optical axis prior to exposing the
wafer. Subsequently, with information regarding the position along
the optical axis, the wafer stage assembly can be controlled to
properly position the wafer along the optical axis. Unfortunately,
previous autofocus systems have been unsatisfactory, in that they
can be slow, overly complex, and/or expensive, and/or such
autofocus systems have only been able to achieve suboptimal
results.
SUMMARY
[0004] The present embodiment is directed toward a detector for
detecting light from a light source. In certain embodiments, the
detector comprises a single array of pixels and a first mask. The
single array of pixels includes a plurality of rows of pixels, and
a plurality of columns of pixels having at least a first active
column of pixels and a spaced apart second active column of pixels.
The first mask covers one of the plurality of columns of pixels to
provide a first masked column of pixels that is positioned between
the first active column of pixels and the second active column of
pixels. Additionally, a charge is generated from the light
impinging on the first active column of pixels, is transferred to
the first masked column of pixels, and subsequently is transferred
to the second active column of pixels.
[0005] In some embodiments, an accumulation of the charge from the
light impinging on the first active column of pixels and the second
active column of pixels generates an output charge.
[0006] In one embodiment, no active column of pixels is positioned
adjacent to another active column of pixels. In certain
embodiments, the first active column of pixels and the second
active column are arranged along a first direction, and are spaced
apart from one another along a second direction that crosses the
first direction. For example, the second direction can be
orthogonal to the first direction.
[0007] In some embodiments, the plurality of columns of pixels
further includes a third active column of pixels that is spaced
apart from the first active column of pixels and the second active
column of pixels. In one such embodiment, the detector further
comprises a second mask that covers one of the plurality of columns
of pixels to provide a second masked column of pixels that is
positioned between the second active column of pixels and the third
active column of pixels. Moreover, in one embodiment, the plurality
of columns of pixels further includes a fourth active column of
pixels that is spaced apart from the first active column of pixels,
the second active column of pixels, and the third active column of
pixels. In such embodiment, the detector can further comprise a
third mask that covers one of the plurality of columns of pixels to
provide a third masked column of pixels that is positioned between
the third active column of pixels and the fourth active column of
pixels.
[0008] In certain embodiments, the detector further comprises a
second mask that covers one of the plurality of columns of pixels
to provide a second masked column of pixels that is positioned
between the first active column of pixels and the second active
column of pixels. In one such embodiment, the detector can further
comprise a third mask that covers one of the plurality of columns
of pixels to provide a third masked column of pixels that is
positioned between the first active column of pixels and the second
active column of pixels.
[0009] In one embodiment, the detector further comprises a lenslet
array that is positioned substantially adjacent to a top surface of
the single array of pixels.
[0010] In some applications, the present embodiment is further
directed toward a position system for measuring the position of a
work piece. In certain embodiments, the position system comprises a
light source that generates (i) a first light beam that is directed
at the work piece at a first time, the first light beam having a
first characteristic, and (ii) a second light beam that is directed
at the work piece at a second time, the second light beam having a
second characteristic that is different than the first
characteristic; and the detector as described above that detects
the first light beam and the second light beam from the light
source.
[0011] In one such embodiment, the first characteristic is a first
wavelength range and the second characteristic is a second
wavelength range that is different than the first wavelength range.
Alternatively, in another such embodiment, the first characteristic
is a first polarization and the second characteristic is a second
polarization that is different than the first polarization. Still
alternatively, in another such embodiment, the first characteristic
includes the first light beam being a measurement beam, and wherein
the second characteristic includes the second light beam being a
reference beam.
[0012] Additionally, in some embodiments, the detector further
comprises a second mask that covers one of the plurality of columns
of pixels to provide a second masked column of pixels that is
positioned between the first active column of pixels and the second
active column of pixels. In such embodiments, the light source
further generates a third light beam that is directed at the work
piece at a third time, the third light beam having a third
characteristic that is different than at least one of the first
characteristic and the second characteristic. Moreover, in such
embodiments, the detector detects the first light beam, the second
light beam and the third light beam from the light source.
[0013] Further, in one such embodiment, the detector further
comprises a third mask that covers one of the plurality of columns
of pixels to provide a third masked column of pixels that is
positioned between the first active column of pixels and the second
active column of pixels. In such embodiment, the light source
further generates a fourth light beam that is directed at the work
piece at a fourth time, the fourth light beam having a fourth
characteristic that is different than at least one of the first
characteristic, the second characteristic and the third
characteristic. Moreover, in such embodiment, the detector detects
the first light beam, the second light beam, the third light beam
and the fourth light beam from the light source.
[0014] Still further, the present embodiment is also directed
toward an exposure apparatus including a stage assembly that
positions a work piece, and the position system as described above
that measures the position of the work piece. The present
embodiment is further directed toward a process for manufacturing a
wafer that includes the steps of providing a substrate, and
transferring a mask pattern to the substrate with the exposure
apparatus as described above.
[0015] In another application, the present embodiment is further
directed toward a method for detecting light from a light source,
the method comprising the steps of (i) providing a single array of
pixels including a plurality of rows of pixels, and a plurality of
columns of pixels having at least a first active column of pixels
and a spaced apart second active column of pixels; (ii) covering
one of the plurality of columns of pixels with a first mask to
provide a first masked column of pixels that is positioned between
the first active column of pixels and the second active column of
pixels; (iii) generating a charge from the light impinging on the
first active column of pixels; (iv) transferring the charge from
the first active column of pixels to the first masked column of
pixels; and (v) subsequently transferring the charge to the second
active column of pixels.
[0016] Additionally, the present embodiment is still further
directed toward a method for measuring the position of a work
piece, the method comprising the steps of (i) generating a first
light beam with a light source, the first light beam having a first
characteristic; (ii) directing the first light beam at the work
piece at a first time, the work piece reflecting the first light
beam; (iii) generating a second light beam with the light source,
the second light beam having a second characteristic that is
different than the first characteristic; (iv) directing the second
light beam at the work piece at a second time, the work piece
reflecting the second light beam; and (v) detecting the first light
beam and the second light beam that are reflected off of the work
piece with the method of claim 14.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] The novel features of embodiments of this invention as to
its structure and its operation, will be best understood from the
accompanying drawings, taken in conjunction with the accompanying
description, in which similar reference characters refer to similar
parts, and in which:
[0018] FIG. 1 is a schematic illustration of an embodiment of an
exposure apparatus, the exposure apparatus including an autofocus
system;
[0019] FIG. 2A is a simplified side view of a work piece, a control
system, and an embodiment of the autofocus system, the autofocus
system including a light source assembly that projects light having
a continuous fringe pattern;
[0020] FIG. 2B is a simplified illustration of an aperture plate
that controls which orders are directed at a working surface of the
work piece to create the continuous fringe pattern of light from
FIG. 2A;
[0021] FIG. 3A is a simplified side illustration of the work piece,
and an embodiment of a measurement light, a reference light, and a
redirector assembly;
[0022] FIG. 3B is a simplified top illustration of the work piece,
the measurement light, the reference light, and the redirector
assembly of FIG. 3A;
[0023] FIG. 3C is a simplified top perspective illustration of the
work piece, the measurement light, the reference light, and the
redirector assembly of FIG. 3A;
[0024] FIG. 4A is a simplified top illustration of the work piece,
and another embodiment of a measurement light, a reference light,
and a portion of a redirector assembly;
[0025] FIG. 4B is a simplified side view of a second redirector of
the redirector assembly of FIG. 4A;
[0026] FIG. 5A is a simplified schematic illustration of an
embodiment of a detector;
[0027] FIG. 5B illustrates the image recorded by active pixels of
the detector of FIG. 5A over time;
[0028] FIG. 5C illustrates the output signal for a single pixel of
the detector of FIG. 5A over time;
[0029] FIG. 6 is a graphical illustration of light from a source
power as a function of time;
[0030] FIG. 7A is a simplified schematic illustration of another
embodiment of a detector;
[0031] FIG. 7B illustrates the image recorded by active pixels of
the detector of FIG. 7A over time;
[0032] FIG. 7C illustrates the output signal for a single pixel of
the detector of FIG. 7A over time;
[0033] FIG. 8A is a simplified schematic illustration of still
another embodiment of a detector;
[0034] FIG. 8B illustrates the image recorded by active pixels of
the detector of FIG. 8A over time;
[0035] FIG. 8C illustrates the output signal for a single pixel of
the detector of FIG. 8A over time;
[0036] FIG. 9A is a simplified schematic top view illustration of
still yet another embodiment of a detector;
[0037] FIG. 9B is a simplified schematic illustration showing
fringes of light and a side view (YZ plane) of the detector of FIG.
9A;
[0038] FIG. 9C is a simplified schematic illustration showing
fringes of light and a side view (XZ plane) of the detector of FIG.
9A;
[0039] FIG. 10 is a graph that illustrates the electronic Nyquist
rate;
[0040] FIG. 11A is a flow chart that outlines a process for
manufacturing a device in accordance with the present embodiment;
and
[0041] FIG. 11B is a flow chart that outlines device processing in
more detail.
DESCRIPTION
[0042] The present embodiment is directed to a chromatic, time
domain integration ("TDI") charge-coupled device ("CCD") that can
be used with a fringe projection type autofocus ("AF") system that
is used to measure the position of a workpiece, e.g. a wafer. As
provided herein, such a fringe projection ("FP") type autofocus
(AF") system can include a light source assembly that generates a
plurality of spaced apart slits of light (or a continuous fringe
pattern of light) wherein a first portion of the slits (or fringes)
of light are concurrently directed at and reflected off of a
working surface of the work piece toward a detector assembly, and a
second portion of the slits (or fringes) of light are concurrently
directed at and reflected off of a redirector assembly toward the
detector assembly. A non-exclusive example of a FP type AF system
is disclosed in PCT Application No. PCT/US12/43186, filed on Jun.
19, 2012, and entitled "AUTOFOCUS SYSTEM WITH REFERENCE
CONFIGURATION". As far as is permitted, the contents of PCT
Application No. PCT/US12/43186 are incorporated herein by
reference. Alternatively, the TDI CCD provided herein can be used
in another type of system.
[0043] FIG. 1 is a schematic illustration of an embodiment of a
precision assembly, namely an exposure apparatus 10. The exposure
apparatus 10 includes an apparatus frame 12, an illumination system
14 (irradiation apparatus), an optical assembly 16, a reticle stage
assembly 18, a wafer stage assembly 20, a position system 22, and a
control system 24. The design of the components of the exposure
apparatus 10 can be varied to suit the design requirements of the
exposure apparatus 10.
[0044] The exposure apparatus 10 is particularly useful as a
lithographic device that transfers a pattern (not shown) of an
integrated circuit from a reticle 26 onto a semiconductor wafer 28.
The exposure apparatus 10 mounts to a mounting base 30, e.g., the
ground, a base, a floor, or some other supporting structure.
[0045] As an overview, the position system 22 includes an autofocus
system 22A that is faster, simpler and less expensive than previous
autofocus systems in order to measure the position of a work piece,
e.g., the wafer 28, along a Z axis with improved accuracy. More
specifically, in certain embodiments, the autofocus system 22A is
uniquely designed to require only a single detector that is able to
capture signals with different spectral properties. Moreover, the
autofocus system 22A utilizes a light source(s) that is
synchronized to the charge transfer of a detector, e.g., the
detector 550 illustrated in FIG. 5A, in such a way that multiple
color images can be captured simultaneously, which is especially
useful for the fringe projection type autofocus system. As a result
thereof, the wafer 28 can be positioned with improved accuracy, and
the exposure apparatus 10 can be used to manufacture higher density
wafers 28.
[0046] A number of Figures include an orientation system that
illustrates an X axis, a Y axis that is orthogonal to the X axis,
and a Z axis that is orthogonal to the X and Y axes. It should be
noted that any of these axes can also be referred to as the first,
second, and/or third axes.
[0047] There are a number of different types of lithographic
devices. For example, the exposure apparatus 10 can be used as a
scanning type photolithography system that exposes the pattern from
the reticle 26 onto the wafer 28 with the reticle 26 and the wafer
28 moving synchronously. Alternatively, the exposure apparatus 10
can be a step-and-repeat type photolithography system that exposes
the reticle 26 while the reticle 26 and the wafer 28 are
stationary. However, the use of the exposure apparatus 10 provided
herein is not limited to a photolithography system for
semiconductor manufacturing. The exposure apparatus 10, for
example, can be used as an LCD photolithography system that exposes
a liquid crystal display device pattern onto a rectangular glass
plate or a photolithography system for manufacturing a thin film
magnetic head.
[0048] The apparatus frame 12 is rigid and supports the components
of the exposure apparatus 10. The apparatus frame 12 illustrated in
FIG. 1 supports the reticle stage assembly 18, the optical assembly
16, the wafer stage assembly 20, and the illumination system 14
above the mounting base 30.
[0049] The illumination system 14 includes an illumination source
32 and an illumination optical assembly 34. The illumination source
32 emits a beam (irradiation) of light energy. The illumination
optical assembly 34 guides the beam of light energy from the
illumination source 32 to the optical assembly 16. The beam
selectively illuminates different portions of the reticle 26 and
exposes the wafer 28.
[0050] The illumination source 32 can be a g-line source (436 nm),
an i-line source (365 nm), a KrF excimer laser (248 nm), an ArF
excimer laser (193 nm), a F.sub.2 laser (157 nm), or an EUV source
(13.5 nm). Alternatively, the illumination source 32 can generate
charged particle beams such as an x-ray or an electron beam. For
instance, in the case where an electron beam is used, thermionic
emission type lanthanum hexaboride (LaB.sub.6) or tantalum (Ta) can
be used as a cathode for an electron gun. Furthermore, in the case
where an electron beam is used, the structure could be such that
either a mask is used or a pattern can be directly formed on a
substrate without the use of a mask.
[0051] The optical assembly 16 projects and/or focuses the light
passing through the reticle 26 to the wafer 28. Depending upon the
design of the exposure apparatus 10, the optical assembly 16 can
magnify or reduce the image illuminated on the reticle 26. The
optical assembly 16 need not be limited to a reduction system. It
could also be a 1.times. (unit magnification) or magnification
system (enlargement system).
[0052] The reticle stage assembly 18 holds and positions the
reticle 26 relative to the optical assembly 16 and the wafer 28. In
FIG. 1, the reticle stage assembly 18 includes a reticle stage 18A
that retains the reticle 26, and a reticle stage mover assembly 18B
that positions the reticle stage 18A and the reticle 26. The
reticle stage mover assembly 18B can be designed to move the
reticle 26 in six degrees of freedom, i.e. along the X, Y and Z
axes, and about the X, Y and Z axes. Alternatively, the reticle
stage mover assembly 18B can be designed to move the reticle 26 in
less than six degrees of freedom.
[0053] Somewhat similarly, the wafer stage assembly 20 holds and
positions the wafer 28 with respect to the projected image of the
illuminated portions of the reticle 26. In FIG. 1, the wafer stage
assembly 20 includes a wafer stage 20A that retains the wafer 28,
and a wafer stage mover assembly 20B that positions the wafer stage
20A and the wafer 28. The wafer stage mover assembly 20B can be
designed to move the wafer 28 in six degrees of freedom, i.e. along
the X, Y and Z axes, and about the X, Y and Z axes. Alternatively,
the wafer stage mover assembly 20B can be designed to move the
wafer 28 in less than six degrees of freedom. In this embodiment,
the wafer 28 can be scanned while the wafer stage assembly 20 moves
the wafer 28 along the Y axis.
[0054] The position system 22 monitors movement of the reticle 26
and the wafer 28 relative to the optical assembly 16 or some other
reference. With this information, the control system 24 can control
the reticle stage assembly 18 to precisely position the reticle 26
and the wafer stage assembly 20 to precisely position the wafer 28.
For example, the position system 22 can utilize multiple laser
interferometers, encoders, autofocus systems, and/or other
measuring devices in addition to the autofocus system 22A.
[0055] In FIG. 1, the position system 22 includes (i) a reticle
measurement system 22B (only a portion is illustrated in FIG. 1)
that monitors the position of the reticle stage 18A and the reticle
26, (ii) a wafer measurement system 22C (only a portion is
illustrated in FIG. 1) that monitors the position of the wafer
stage 20A and the wafer 28 along the X and Y axes, and about the Z
axis, and (iii) the autofocus system 22A that maps the topography
of the wafer 28 relative to the optical assembly 16 along the Z
axis (i.e. along an optical axis 16A of the optical assembly 16),
about the X axis, and about the Y axis prior to exposure with
improved accuracy. As a result thereof, the wafer stage assembly 20
can be controlled to position the wafer 28 with improved
accuracy.
[0056] In certain embodiments, the autofocus system 22A can be
fixedly secured to the optical assembly 16 or to a support frame
which supports the optical assembly 16. As provided herein, the
autofocus system 22A includes a reference system 36 that provides a
reference signal that relates to the measurement of everything that
is changing in the autofocus system 22A except for the position of
the wafer 28 along the optical axis 16A, and a measurement system
38 that provides a measurement signal that relates to the
measurement of everything changing in the autofocus system 22A
including the position of the wafer 28 along the optical axis 16A.
By subtracting the reference signal from the measurement signal,
the position of the wafer 28 along the optical axis 16A is
determined, thereby reducing the stability requirements on much of
the components of the autofocus system 22A.
[0057] In this embodiment, the reference system 36 and the
measurement system 38 are secured to and monitor the position of
the wafer 28 relative to the optical assembly 16. Alternatively,
these systems 36, 38 can be secured to and monitor the position of
the wafer 28 relative to another reference.
[0058] The control system 24 is connected to the reticle stage
assembly 18, the wafer stage assembly 20, and the position system
22. The control system 24 receives information from the position
system 22 and controls the stage assemblies 18, 20 to precisely
position the reticle 26 and the wafer 28. The control system 24 can
include one or more processors and circuits.
[0059] FIG. 2A is a simplified side view of a work piece 200, a
control system 224, and an embodiment of an autofocus system 222
that measures the position of a working surface 200A of the work
piece 200 along the Z axis, about the X axis and about the Y axis.
In this embodiment, for example, the work piece 200 can be the
wafer 28 (illustrated in FIG. 1) and the working surface 200A is
the surface where the features are transferred. Alternatively, the
autofocus system 222 can be used to monitor the position of other
types of work pieces 200 (e.g., the reticle 26 illustrated in FIG.
1) during manufacturing and/or inspection.
[0060] In certain embodiments, the position of the work piece 200
along the Z axis for each X, Y position can be premapped prior to
exposing the work piece 200. With this design, for each X, Y
position of the work piece 200, the control system 224 can be
controlled to make the appropriate adjustment to the Z position of
the work piece 200 based on the premapped information.
Alternatively, for example, the autofocus system 222 can
continuously measure the position of the work piece 200 along the Z
axis. With this design, the stage mover assembly 20 (illustrated in
FIG. 1) can be controlled to make real time adjustments to the Z
position of the work piece 200 based on the measurements from the
autofocus system 222.
[0061] In FIG. 2A, the autofocus system 222 is a fringe projection
type system that includes a reference system 236 and a measurement
system 238. The design and positioning of each of these components
can be varied to achieve the measurement requirements of the
autofocus system 222. In FIG. 2A, the reference system 236 and the
measurement system 238 share a common light source assembly 240,
and a common detector assembly 242. The common detector assembly
242 can be preferred since it reduces errors due to any
instabilities of the detector assembly 242. Alternatively, for
example, the reference system 236 and the measurement system 238
can have independent light source assemblies, and detector
assemblies. As provided herein, in one embodiment, the light source
assembly 240 projects light that results in a sinusoidal irradiance
pattern, with such sinusoidal irradiance pattern being usable with
the present autofocus system 222. A discussion of a sinusoidal
irradiance fringe pattern autofocus system is contained in U.S.
application Ser. No. 13/066,741, filed on Apr. 22, 2011. As far as
permitted, the contents of U.S. application Ser. No. 13/066,741 are
incorporated herein by reference.
[0062] Additionally, in this embodiment, the reference system 236
includes a redirector assembly 244 that is used to provide the
reference signal.
[0063] The light source assembly 240 generates one or more beams of
light that are directed at the workpiece 200 and the redirector
assembly 244. Further, the detector assembly 242 measures the light
reflected off of the workpiece 200 and the redirector assembly 244.
In FIG. 2A, the light source assembly 240 projects light that
results in a sinusoidal irradiance pattern that includes a
plurality of fringes of light 246 on the work piece 200 and the
redirector assembly 244. In one embodiment, the light source
assembly 240 includes (i) a light source 248A that generates light
248B, (ii) a lens 248C that collimates the light 248B from the
light source 248A, (iii) a grating 248D that creates at least three
plane waves (-1, 0, +1) for each wavelength, (iv) a lens 248E that
focuses the light from the grating 248D, (v) an aperture plate 248F
(illustrated in detail in FIG. 2B) that blocks the zero order plane
wave and all higher orders while allowing the -1 and +1 waves to
pass therethrough, and (iv) a lens 248G that directs the -1 and +1
waves onto the work piece 200 and the redirector assembly 244,
where they create a sinusoidal irradiance pattern of light 246.
[0064] Additionally, as discussed in greater detail herein below,
in certain embodiments, the light source 248A is a strobed light
source that can generate and/or provide the light 248B in a strobed
manner. As utilized herein, a strobed light source or a strobed
light is one where one or more characteristics of the light 248B
are changed over time in discrete increments (e.g., at time
t.sub.0, at time t.sub.1, at time t.sub.2, etc.). For example, in
one embodiment, the wavelength (i.e. the color) of the light 248B
can be changed over time such that different wavelengths (colors)
or wavelength ranges of light 248B are generated at different
discrete times. In one such, non-exclusive embodiment, the light
source 248A can include four separate light emitting diodes
("LEDs") and each LED can generate light over a different
wavelength range or wavelength spectrum. Thus, in such embodiment,
the light 248B can include four different beams with each beam
having a different wavelength range or wavelength spectrum.
Additionally and/or alternatively, in one embodiment, the
polarization of the light 248B can be changed over time such that
different polarizations of light 248B are generated at different
discrete times. Still alternatively, other characteristics of the
light 248B can be changed at different discrete times.
[0065] It should be noted that the fringes of light 246 can be used
to measure changes in the height of the work piece 200 because the
phase of the fringes of light 246 changes as the height of the work
piece 200 changes. The phase of the fringes of light 246 changes as
the height of the work piece 200 changes due to such factors as the
pitch of the sinusoidal irradiance pattern and the high angle of
incidence of the fringes of light 246 impinging on the work piece
200.
[0066] In the embodiment illustrated in FIG. 2A, the grating 248D
is imaged to the work piece 200 and the redirector assembly 244 via
an afocal relay, and all wavelengths generated by the light source
248A create a fringe pattern with the same spatial frequency on the
work piece 200 and the redirector assembly 244, and the plane waves
for each wavelength have different angles relative to the optical
axis (e.g., the Z axis) in the optical space near the work piece
200 and the redirector assembly 244. In this design, in the space
between the lens 248E and the lens 248G, the beams from the
multiple wavelengths are converging, focusing, and then
diverging.
[0067] In one embodiment, (i) a first portion of the fringes of
light 246, hereinafter referred to as measurement light 246A or
measurement beam, is imaged onto the work piece 200; and (ii) a
second portion of the fringes of light 246, hereinafter referred to
as reference light 246B or reference beam, is projected onto the
redirector assembly 244. In FIG. 2A, the fringes of the light 246
that are farthest out of the page along the Y axis is the reference
light 246B, while the fringes of light 246 that are into the page
along the Y axis is the measurement light 246A. With this design,
the redirector assembly 244 picks off and redirects some of the
fringes of light 246 before they are imaged onto the work piece
200.
[0068] The detector assembly 242 detects the measurement light 246A
that is reflected off of the work piece 200 and the reference light
246B that is reflected off of the redirector assembly 244. In one
embodiment, the detector assembly 242 includes (i) a lens 250A that
focuses the measurement light 246A that is reflected off of the
work piece 200 and the reference light 246B that is reflected off
of the redirector assembly 244, (ii) an aperture 250B that blocks
light diffracted by the patterns that exist on the wafer, (iii) a
lens 250C that focuses the light that passes from the aperture
250B, and (iv) a detector 250D. With this design, the same detector
250D is used to measure both the measurement light 246A that is
reflected off of the work piece 200 and the reference light 246B
that is reflected off of the redirector assembly 244. Thus, the
detector 250D can provide to the control system 224 a measurement
signal that relates to the measurement light 246A that is reflected
off of the work piece 200 and a reference signal that relates to
the reference light 246B that is reflected off of the redirector
assembly 244. In some embodiments, the detector 250D is a
charge-coupled device. For example, in one such embodiment, the
detector 250D can be a chromatic, time domain integration ("TDI")
charge-coupled device ("CCD").
[0069] As noted above, in certain embodiments, the light source
248A can be a strobed light source that can generate and/or provide
the light 248B in a strobed manner. With this design, the detector
250D can be utilized to provide the measurement signal and the
reference signal to the control system 224 in an alternating
manner. Stated in another fashion, the measurement signal and the
reference signal can be effectively strobed in time as the light
source 248A is able to alternatingly provide the measurement light
246A (i.e. that is reflected off of the work piece 200) and the
reference light 246B (i.e. that is reflected off of the redirector
assembly 244) that are reflected and/or redirected toward the
detector 250D.
[0070] Additionally, in some embodiments, the light, i.e. the
measurement light 246A and the reference light 246B, that is
incident on the detector 250D can be directed at the detector 250D
so as to have a grazing angle of incidence of between approximately
thirty and eighty degrees relative to the detector normal.
Additionally, the grazing angle of incidence can be fixed for a
given design (i.e. the angle does not vary for a given fringe
projection system). Moreover, as illustrated, the grazing angle of
incidence is about the Y-axis. Alternatively, the light, i.e. the
measurement light 246A and the reference light 246B, that is
incident on the detector 250D can be directed at the detector 250D
at a different angle.
[0071] As provided herein, the reference signal relates to the
measurement of everything that is changing in the autofocus system
222 except for the position of the work piece 200 along the Z axis,
and the measurement signal relates to the measurement of everything
changing in the autofocus system 222 including the position of the
work piece 200 along the Z axis. With this design, the control
system 224 can subtract the reference signal from the measurement
signal to determine the position of the work piece 200 along the Z
axis.
[0072] In one embodiment, the redirector assembly 244 includes a
first redirector 252 and a second redirector 254. These components
are described in more detail below in reference to FIGS. 3A-3C. In
one non-exclusive embodiment, the first redirector 252 and the
second redirector 254 can be fixedly secured to the optical
assembly 16 (illustrated in FIG. 1) with a redirector bracket 55
(illustrated in FIG. 1). Alternatively, the first redirector 252
and the second redirector 254 may be fixedly secured to the support
frame which supports the optical assembly 16.
[0073] It should be noted that the present embodiment can be
designed for use without the reference assembly.
[0074] FIG. 2B is a simplified illustration of the aperture plate
248F and the light diffracted by the grating 248D that has been
focused by the lens 248E in the plane of the aperture plate 248F
from FIG. 2A. This Figure illustrates that four separate wavelength
beams 256A, 256B, 256C, 256D, each with a -1, 0, +1 order plane
wave, are focused in the plane of the aperture plate 248F, and that
the aperture plate 248F blocks the zero order light for each of the
beams 256A, 256B, 256C, 256D, while the +1 order light and the -1
order light for each of the beams 256A, 256B, 256C, 256D are
allowed to pass the aperture plate 248D. In this embodiment, two
orders (e.g., the +1, -1) for three of the beams 256A, 256B, 256C
are directed at the work piece 200, and two orders (e.g., the +1,
-1) of the fourth beam 256D are directed at the redirector assembly
244.
[0075] FIG. 3A is a simplified side illustration, FIG. 3B is a
simplified top illustration, and FIG. 3C is a simplified top
perspective view of the work piece 300, the measurement light 346A
directed at the work piece 300, the reference light 346B directed
at the redirector assembly 344, and one embodiment of the first
redirector 352 and the second redirector 354 of the redirector
assembly 344. As illustrated in these Figures, the reference light
346B can be displaced and spaced apart along the Y axis (the wafer
scan direction) from the measurement light 346A prior to the
measurement light 346A being incident on the work piece 300 and the
reference light 346B being incident on the first redirector
352.
[0076] In this embodiment, (i) the reference light 346B from the
light source assembly 240 (illustrated in FIG. 2A) is directed at
the first redirector 352, (ii) the first redirector 352 redirects
the reference light 346B at the second redirector 354, (iii) the
second redirector 354 redirects the reference light 346B back to
the first redirector 352, and (iv) the first redirector 352
redirects the reference light 346B back to the detector assembly
242 (illustrated in FIG. 2A).
[0077] In one embodiment, the first redirector 352 is a fold mirror
that redirects the reference light 346B at an angle relative to the
input light. With this design, the first redirector 352 folds the
reference light 346B into a beam plane 358 that is approximately
parallel to, spaced apart from, and positioned above a working
surface plane 300B of the working surface 300A of the work piece
300. In certain embodiments, the first redirector 352 redirects the
reference light 346B out of the XZ plane. The XZ plane may be
regarded as a first plane in which the measurement beam traveled.
For example, the first redirector 352 can be made from glass, in
the shape of a long, right triangle prism (e.g., a long prism with
a right triangular shaped cross-section). Alternatively, the first
redirector 352 can be made from metal, with the hypotenuse highly
polished. This would allow for easier mounting of the first
redirector 352. Still alternatively, the first redirector 352 can
include a mirror mounted to a metal mount, again for easier
mounting. In one non-exclusive embodiment, the first redirector 352
has a width of approximately five millimeters.
[0078] As illustrated in FIG. 3A, a center of the reference light
346B is incident on the first redirector 352 at a first redirector
area 360, and the first redirector area 360 is positioned a first
separation distance 362 away from the working surface 300A along
the Z axis. In alternative, non-exclusive embodiments, the first
separation distance 362 can be approximately 1.5, 2.0, 2.5, or 3.0
millimeters.
[0079] The second redirector 354 can be a reflector or mirror that
is positioned away from the first redirector 352 along the beam
plane 358 (e.g., along the Y axis) such that it is optically
coincident with the working surface 300A of the work piece 300.
With this design, the second redirector 354 reflects the reference
light 346B back to the first redirector 352 along the beam plane
358 that is parallel to, and spaced apart from the working surface
plane 300B. Further, the reference light 346B is incident on the
second redirector 354 at a second redirector area 364 positioned on
the beam plane 358, and the second redirector area 364 is spaced
apart a second separation distance 366 from the first redirector
area 360 along the beam plane 358. Moreover, in certain
embodiments, the second separation distance 366 is equal to or
approximately equal to the first separation distance 362. This is
important because the second redirector 354 is not defocused
relative to the working surface 300A of the work piece 300. Stated
in another fashion, when the second separation distance 366 is
equal to the first separation distance 362, the reference light
346B travels the same distance via the redirectors 352, 354 as it
would have if it was instead incident on the working surface 300A.
As a result thereof, the same detector assembly 242 can be used for
both the measurement light 346A and the reference light 346B. This
simplifies the receiving side optics.
[0080] In one non-exclusive embodiment, the second redirector 354
can be made from glass, in the shape of a long rectangular bar.
Alternatively, the second redirector 354 can be made from metal,
with a side that is highly polished. This would allow for easier
mounting of the second redirector 354. Still alternatively, the
second redirector 354 can include a mirror mounted to a metal
mount, again for easier mounting.
[0081] In certain embodiments, the reference light 346B is incident
at a grazing angle of incidence to the first redirector 352. For
this reason, the first redirector 352 may be required to be quite
long, depending on the size of the first separation distance 362,
the numerical aperture of the reference light 346B, and the length
of the second redirector 354. Generally, the smaller the first
separation distance 362, the smaller the length that the first
redirector 352 is required to be. As non-exclusive examples, the
first redirector 352 and the second redirector 354 can be
approximately 350, 400, 450 or more millimeters in length (L).
[0082] In this embodiment, the reference light 346B is not
perfectly collinear with the measurement light 346A. However, the
reference light 346B will still provide a high degree of
correction, because the lateral displacement (along the Y axis in
this example) is not much and the reference light 346B goes through
all the same components of the light source assembly 240 and the
detector assembly 242.
[0083] Importantly, in the design described above, the reference
light 346B does not travel through one or more prisms (not shown).
The problem with using one or more prisms is that it will add a
glass path and dispersion that will only be in the path of the
reference light 346B and not in the path of the measurement light
346A. This makes it difficult for the reference and measurement
lights to have equivalent optical paths. Thus, in certain
embodiments, the proposed autofocus system 222 (illustrated in FIG.
2A) has no glass path to introduce a different level of dispersion
in the reference light 346B when compared to the measurement light
346A.
[0084] FIG. 4A is a simplified top illustration of the work piece
400, the first redirector 452 and the second redirector 454 of the
redirector assembly 444, an embodiment of the measurement light
446AB imaged on the work piece 400, and an embodiment of the
reference light 446BB directed at the first redirector 452.
Additionally, FIG. 4B is a side view of the second redirector 454
of FIG. 4A. In this embodiment, (i) the light source assembly 240
(as illustrated in FIG. 2A) generates a plurality of fringes of
light, (ii) a first portion of the fringes of light (referred to as
the measurement light 446AB) are concurrently directed at and
reflected off of the work piece 400, and (iii) a second portion of
the fringes of light (referred to as the reference light 446BB) are
concurrently directed at and reflected off of the redirector
assembly 444. It should be noted that the reference light 446BB
will actually be significantly defocused on the first redirector
452 and will not appear as a plurality of fringes of light on the
first redirector 452.
[0085] Moreover, in this embodiment, (i) the measurement light
446AB is simultaneously imaged onto the work piece 400 at a
plurality of measurement areas 455A-455M positioned along the X
axis, and the detector assembly 242 (illustrated in FIG. 2A)
detects the measurement light 446AB reflected off of the work piece
400 and generates a measurement signal for each of the measurement
areas 455A-455M; and (ii) the reference light 446BB is
simultaneously imaged onto the second redirector 454 at a plurality
of reference areas 457A-457M positioned along the X axis, and the
detector assembly 242 detects the reference light 446BB reflected
off of the second redirector 454 and generates a reference signal
for each of the reference areas 457A-457M. Additionally, in this
embodiment, (i) the work piece 400 has a surface length 470
measured along the X axis; (ii) the plurality of measurement areas
455A-455M are positioned along substantially the entire surface
length; and (iii) the reference areas 457A-457M are positioned
along a reference length 472 that is approximately equal to the
surface length 470. With this design, the reference areas 457A-457M
are near the measurement areas 455A-455M, and the many reference
areas 457A-457M that are spread along the surface length 470
correspond, one to one, to the many measurement areas 455A-455M,
such that every measurement area 455A-455M has a corresponding,
unique reference area 457A-457M.
[0086] In this embodiment, the measurement light 446AB is
substantially continuous across the work piece 400, and the
reference light 446BB is substantially continuous along the
redirector assembly 444. In this embodiment, the parsing into
individual measurement areas 455A-455M and individual reference
areas 457A-457M happens with the spatial discretization at the
detector (not shown in FIGS. 4A and 4B). Thus, with this system,
there is a plurality of discrete measurement areas 455A-455M and a
plurality of discrete reference areas 457A-457M.
[0087] The number of measurement areas 455A-455M and the number of
reference areas 457A-457M can be varied. In certain embodiments, as
noted above, the system is designed so that every measurement area
455A-455M has a corresponding reference area 457A-457M. With this
design, a reference signal is generated for each measurement
signal, and there is a one to one ratio of measurement signals and
reference signals. Stated in another fashion, in such embodiments,
there is a separate, independent, corresponding reference signal
for each measurement signal. As provided herein, with this design,
the control system 224 (illustrated in FIG. 2A) can utilize simple
subtraction between each corresponding reference signal and
measurement signal for processing. For example, the control system
224 can (i) subtract the first reference signal from the first
measurement signal to determine the position of the work piece 400
at the first measurement area 455A; (ii) subtract the second
reference signal from the second measurement signal to determine
the position of the work piece 400 at the second measurement area
455B; and (iii) subtract the third reference signal from the third
measurement signal to determine the position of the work piece 400
at the third measurement area 455C. This process is repeated to
determine the position of each of the measurement areas
455A-455M.
[0088] It should be noted that (i) any of the measurement areas
455A-455M can be referred to as a first, second, third, etc.
measurement area 455A-455M, (ii) the corresponding measurement
signals can be referred to as a first, second, third, etc.
measurement signal, (iii) any of the reference areas 457A-457M can
be referred to as a first, second, third, etc. reference area
457A-457M, and (iv) the corresponding reference signals can be
referred to as a first, second, third, etc. reference signal.
Further, in certain embodiments, each corresponding measurement
area 455A-455M and reference area 457A-457M are approximately
aligned along the Y axis.
[0089] FIG. 5A is a simplified schematic illustration of an
embodiment of a detector 550 that is usable as part of the
autofocus system 222 (illustrated in FIG. 2A). The design of the
detector 550 can be varied to suit the specific requirements of the
autofocus system 222. For example, in one embodiment, as
illustrated in FIG. 5A, the detector 550 can be a chromatic, TDI
CCD that can be used with a fringe projection type autofocus system
that is used to measure the position of a work piece, e.g., a wafer
28 (illustrated in FIG. 1). Alternatively, the detector 550, i.e.
the TDI CCD, can be used in another type of system.
[0090] As provided herein, for a fringe projection type AF system,
it is essential that different spectral bands are measured for the
same location on the wafer 28. The present embodiment allows this
to be done using a modified TDI CCD detector 550.
[0091] A TDI CCD detector, such as being used as part of the
present embodiment, transfers a charge across the front of the CCD
in a TDI direction (e.g., left to right in FIG. 5A) synchronously
to the image motion, as such devices are typically used with a
moving object. This allows a brighter image to be obtained for a
given amount of irradiance (power per unit area). For example, in
the embodiment shown in FIG. 5A, the +Y direction can be defined as
the TDI direction. Accordingly, in such embodiment, the X direction
would be perpendicular to the TDI direction. Thus, in this
embodiment, the charge is transferred from left to right as
illustrated in FIG. 5A. Additionally, TDI CCD detectors can be used
with a moving object.
[0092] As illustrated in FIG. 5A, the detector 550 includes a
rectangular array of pixels 574 comprising a plurality of rows of
pixels 574R (each row extends from left to right in FIG. 5A, i.e.
in the +Y direction) and a plurality of columns of pixels 574C
(each column extends from top to bottom in FIG. 5A, i.e. in the -X
direction). It should be noted that the number of pixels 574, the
number of rows of pixels 574R, and the number of columns of pixels
574C specifically illustrated in FIG. 5A is for purposes of
demonstration only, and is not necessarily representative of a
desired number of pixels 574, rows of pixels 574R and/or columns of
pixels 574C. More particularly, the number of pixels 574, rows of
pixels 574R and/or columns of pixels 574C can be varied as desired.
For example, in one non-exclusive embodiment, the detector 550 can
include 8192 rows of pixels 574R. Alternatively, the detector 550
can include greater than or less than 8192 rows of pixels 574R.
[0093] Additionally, as illustrated, the detector 550 includes a
plurality of masks 576 that are fixed relative to the pixels 574
and that extend over and cover entire columns of pixels 574C. With
this design, the detector 550 includes a plurality of active
columns 574AC (i.e. uncovered or unmasked columns, shown in white),
and a plurality of masked columns 574MC (shown in black). As
illustrated, the plurality of active columns 574AC and the
plurality of masked columns 574MC are each arranged along a first
direction (i.e. the vertical direction as illustrated in FIG. 5A).
In certain embodiments, at least every other column of pixels 574C
is covered by one of the plurality of masks 576, such that no
active columns 574AC are positioned adjacent to another active
column 574AC, i.e. each of the active columns 574AC is spaced apart
from each of the other active columns 574AC in a second direction
(i.e. the horizontal direction in FIG. 5A) that is substantially
orthogonal to the first direction, with at least one masked column
574MC positioned therebetween. Stated in another manner, in such
embodiments, no two active columns 574AC are positioned adjacent to
one another along the second direction.
[0094] In the embodiment illustrated in FIG. 5A, the active columns
574AC and the masked columns 574MC alternate, such that there is
one masked column 574MC for every active column 574AC. Thus, except
for the end columns, a single masked column 574MC is positioned
between two active columns 574AC, and a single active column 574AC
is positioned between two masked columns 574MC. Alternatively, more
than one masked column 574MC can be positioned between the active
columns 574AC. For example, in certain non-exclusive alternative
embodiments, the detector 550 can include two, three, four or five
masked columns 574MC for every active column 574AC.
[0095] The type of mask used for each masked column 574MC can be
varied according to the characteristics of the light. For example,
the mask can be made of a material that inhibits and blocks the
transmission of the light. Suitable materials for the mask include
aluminum and silver.
[0096] Further, with the unique design of the detector 550, as
provided herein, a charge is initially generated from light, e.g.,
light 248B (illustrated in FIG. 2A) from the light source 248A
(illustrated in FIG. 2A), impinging on a first active column of
pixels 574AC, i.e. the left-most active column 574AC in FIG. 5A.
The charge is then transferred to the adjacent masked column of
pixels 574MC, and subsequently the charge is transferred to the
adjacent active column of pixels 574AC. The process of transferring
the charge in such a manner is continued until the charge reaches
the right end of the array of pixels 574, i.e. the right-most
column of pixels 574C. Ultimately, an output charge, e.g., the
charge that gets digitized in a digital camera, is generated due to
an accumulation of charge from the light 248B impinging on each of
the active columns of pixels 574AC as the light 248B and/or charge
is transferred from left-to-right, i.e. in the TDI direction,
across the array of pixels 574.
[0097] Moreover, the detector 550 can include a wire (not
illustrated for purposes of clarity) that is coupled and/or secured
to an end of each row of pixels 574R so as to effectively capture a
signal, e.g., an analog signal, for each row of pixels 574R as a
function of time, as the pixels 574 shift to the right (in the +Y
direction as illustrated in FIG. 5A) over time. Thus, in this
embodiment, the signal for each row of pixels 574R is captured
and/or read at the right end of the row of pixels 574R. The analog
signal on this wire is converted to a digital signal using an
analog to digital converter (ADC).
[0098] FIG. 5B illustrates the image recorded by the active columns
of the detector 550 of FIG. 5A over time. In particular, FIG. 5B
shows the image recorded by those active pixels for times t.sub.0
through t.sub.3 as the light source 248A (illustrated in FIG. 2A)
provides light 248B (illustrated in FIG. 2A) to illuminate the
detector 550.
[0099] In one embodiment, the light source 248A effectively
illuminates the pixels on the detector 550.
[0100] In one embodiment, as provided above, the light source 248A
is strobed, such that the wavelength (or wavelength range) of the
light 248B provided by the light source 248A can be selectively
adjusted in discrete increments over time. Stated another way, the
wavelength (or wavelength range) of the light 248B provided by the
light source 248A can be strobed for times t.sub.0, t.sub.1,
t.sub.2, t.sub.3, etc. For example, as shown in FIG. 5B, at time
t.sub.0, the light source 248A provides light at wavelength
.lamda..sub.2 (i.e. .lamda..sub.2 is on); at time t.sub.1, the
light source 248A provides light at wavelength .lamda..sub.1 (i.e.
.lamda..sub.1 is on); at time t.sub.2, the light source 248A
provides light at wavelength .lamda..sub.2 (i.e. .lamda..sub.2 is
on); at time t.sub.3, the light source 248A provides light at
wavelength .lamda..sub.1 (i.e. .lamda..sub.1 is on); etc.
Additionally and/or alternatively, other characteristics of the
light 248B generated by the light source 248A can be selectively
adjusted in discrete increments over time. For example, the
polarization and/or other characteristics of the light 248B
generated by the light source 248A can be adjusted in discrete
increments over time.
[0101] Moreover, the rate at which the light source 248A is strobed
can vary depending on the overall capabilities of the system. For
example, in one non-exclusive embodiment, the light source 248A is
strobed at a rate of sixty-eight kHz (or 68,000 lines per second).
Alternatively, the light source 248A can be strobed at a different
rate that is greater than or less than sixty-eight kHz.
[0102] Further, it should be noted that as the number of masked
columns 574MC per active column 574AC increases, the number of
different wavelengths, wavelength ranges, polarizations, etc. of
light 248B that can be used also increases. For example, in the
embodiment illustrated in FIGS. 5A and 5B, with one masked column
574MC per active column 574AC, two different wavelengths,
wavelength ranges, and/or polarizations, etc. of light 248B can be
used from the light source 248A. Alternatively, in certain
non-exclusive alternative embodiments, if the detector 550 includes
two masked columns for each active column, up to three different
wavelengths, wavelength ranges, and/or polarizations, etc. of light
248B can be used from the light source 248A; if the detector 550
includes three masked columns for each active column, up to four
different wavelengths, wavelength ranges, and/or polarizations,
etc. of light 248B can be used from the light source 248A; if the
detector 550 includes four masked columns for each active column,
up to five different wavelengths, wavelength ranges, and/or
polarizations, etc. of light 248B can be used from the light source
248A; and if the detector 550 includes five masked columns for each
active column, up to six different wavelengths, wavelength ranges,
and/or polarizations, etc. of light 248B can be used from the light
source 248A.
[0103] It should be further noted that the purpose of the masked
columns 574MC (illustrated in FIG. 5A) of pixels is to shield the
.lamda..sub.1 signal from .lamda..sub.2 light when .lamda..sub.2 is
on, and vice versa at the next TDI clock cycle.
[0104] Additionally, for purposes of demonstrating the output of
the present embodiment, FIG. 5B further isolates a single pixel
(i.e. in the X direction) and labels that as Pixel "N" (shown as a
dashed rectangular box).
[0105] FIG. 5C illustrates the output signal for a single pixel,
i.e. Pixel "N", of the detector 550 of FIGS. 5A and 5B over time.
In this case, every other data point in time corresponds to
.lamda..sub.1, while the other interleaved set of data points
corresponds to .lamda..sub.2. Assuming the object (in the FP AF
system this can be the wafer 28 (illustrated in FIG. 1)) is moving
synchronously to the charge transfer, the result is two images of
nearly the same locations on the wafer 28 in x and y interleaved in
time. The extent to which the two images are the same depends on
the characteristics of the entire optical system, including the
optics resolution, for example. The two images are then combined to
accurately determine the position of the wafer 28. Stated another
way, in this embodiment, the values measured at a particular
location from each of the different wavelengths of light can be
combined, e.g., by the control system 224 (illustrated in FIG. 2A),
to accurately determine the position of the wafer 28. Additionally,
it should be noted that the output signal that is provided from the
detector 550 depends on the fringe phase for each wavelength that
is provided by the light source 248A (illustrated in FIG. 2A), with
the fringe phase varying as the position, i.e. the height, of the
wafer 28 varies. It should be noted that it is not a requirement
that the object is moving synchronously to the charge transfer in
the TDI region. In the case where the object is not synchronized to
the charge transfer, the locations measured on the object by the
two images are slightly different. This difference depends on the
resolution of the optical system of FIG. 2A, along with other
system parameters.
[0106] FIG. 6 is a graphical illustration of the light 248B from
the source power, i.e. the source irradiance or light source 248A
(illustrated in FIG. 2A), as a function of time. More specifically,
FIG. 6 graphically illustrates that at time t.sub.0, the light has
a wavelength of .lamda..sub.2; at time t.sub.1, the light has a
wavelength of .lamda..sub.1; at time t.sub.2, the light has a
wavelength of .lamda..sub.2; at time t.sub.3, the light has a
wavelength of .lamda..sub.1; etc. In one non-exclusive embodiment,
the light source 248A can be strobed at a rate of sixty-eight kHz
(or 68,000 lines per second). Alternatively, the light source 248A
can be strobed at a different rate, i.e. at a rate higher or lower
than sixty-eight kHz.
[0107] FIG. 7A is a simplified schematic illustration of another
embodiment of a detector 750. The detector 750 is somewhat similar
to the detector 550 illustrated and described above in relation to
FIG. 5A. In particular, the detector 750 can again be a chromatic,
TDI CCD that can be used with a fringe projection type autofocus
system, e.g., the autofocus system 222 (illustrated in FIG. 2A),
that is used to measure the position of a work piece, e.g., a wafer
28 (illustrated in FIG. 1). Additionally, the detector 750 again
includes a rectangular array of pixels 774 comprising a plurality
of rows of pixels 774R (each row extends from left to right in FIG.
7A, i.e. in the +Y direction) and a plurality of columns of pixels
774C (each column extends from top to bottom in FIG. 7A, i.e. in
the -X direction). Further, the detector 750 again includes a
plurality of masks 776 that are fixed relative to the pixels 774
and that extend over and cover entire columns of pixels 774C. With
this design, the detector 750 includes a plurality of active
columns 774AC (i.e. uncovered or unmasked columns, shown in
white)), and a plurality of masked columns 774MC (shown in
black).
[0108] However, in this embodiment, there are three masked columns
774MC for every active column 774AC. This allows up to four
different spectral signals to be collected using a single TDI
chip.
[0109] Further, in this embodiment, a charge is initially generated
from light, e.g., light 248B (illustrated in FIG. 2A) from the
light source 248A (illustrated in FIG. 2A), impinging on a first
active column of pixels 774AC, i.e. the left-most active column
774AC in FIG. 7A. The charge is then transferred to the three
adjacent masked columns of pixels 774MC, and subsequently the
charge is transferred to the adjacent active column of pixels
774AC. The process of transferring the charge in such a manner is
continued until the charge reaches the right end of the array of
pixels 774, i.e. the right-most column of pixels 774C. Ultimately,
an output charge is generated due to an accumulation of charge from
the light 248B impinging on each of the active columns of pixels
774AC as the light 248B and/or charge is transferred from
left-to-right, i.e. in the TDI direction, across the array of
pixels 574.
[0110] FIG. 7B illustrates the image recorded by active columns of
the detector 750 of FIG. 7A over time. In particular, FIG. 7B shows
the image recorded by those active pixels for times t.sub.0 through
t.sub.3 as the light source 248A (illustrated in FIG. 2A) provides
light 248B (illustrated in FIG. 2A) to illuminate the detector
750.
[0111] Similar to the previous embodiment, the light source 248A
(illustrated in FIG. 2A) is again strobed, such that the wavelength
of the light provided by the light source 248A is selectively
adjusted in discrete increments over time. Stated another way, the
wavelength of the light provided by the light source 248A can be
strobed for times t.sub.0, t.sub.1, t.sub.2, t.sub.3, etc. For
example, as shown in FIG. 7B, at time t.sub.0, the light source
248A provides light at wavelength .lamda..sub.1 (i.e. .lamda..sub.1
is on); at time t.sub.1, the light source 248A provides light at
wavelength .lamda..sub.2 (i.e. .lamda..sub.2 is on); at time
t.sub.2, the light source 248A provides light at wavelength
.lamda..sub.3 (i.e. .lamda..sub.3 is on); at time t.sub.3, the
light source 248A provides light at wavelength .lamda..sub.4 (i.e.
.lamda..sub.4 is on); etc. Additionally and/or alternatively, other
characteristics of the light 248B generated by the light source
248A can be selectively adjusted in discrete increments over time.
For example, the polarization and/or other characteristics of the
light 248B generated by the light source 248A can be adjusted in
discrete increments over time.
[0112] Moreover, the rate at which the light source 248A is strobed
can vary depending on the overall capabilities of the system. For
example, in one non-exclusive embodiment, the light source 248A is
strobed at a rate of sixty-eight kHz (or 68,000 lines per second).
Alternatively, the light source 248A can be strobed at a different
rate that is greater than or less than sixty-eight kHz.
[0113] Additionally, for purposes of demonstrating the output of
the present embodiment, FIG. 7B again isolates a single pixel (i.e.
in the X direction) and labels that as Pixel "N" (shown as a dashed
rectangular box).
[0114] FIG. 7C illustrates the output signal for a single pixel,
i.e. Pixel "N" of the detector 750 of FIGS. 7A and 7B over time. In
this case, the data points correspond consecutively to
.lamda..sub.1, .lamda..sub.2, .lamda..sub.3 and .lamda..sub.4, with
the pattern repeating itself over time. Assuming the object (in the
FP AF system this is the wafer 28 (illustrated in FIG. 1)) is
moving synchronously to the charge transfer, the result is four
images of nearly the same locations on the wafer 28 in x and y
interleaved in time. The four images are then combined to
accurately determine the position of the wafer 28. Stated another
way, in this embodiment, the values measured at a particular
location from each of the different wavelengths of light can be
combined, e.g., by the control system 224 (illustrated in FIG. 2A),
to accurately determine the position of the wafer 28. Additionally,
it should be noted that the output signal that is provided from the
detector 750 depends on the fringe phase for each wavelength that
is provided by the light source 248A (illustrated in FIG. 2A), with
the fringe phase varying as the position, i.e. the height, of the
wafer 28 varies. It should be noted that it is not a requirement
that the object is moving synchronously to the charge transfer in
the TDI region. In the case where the object is not synchronized to
the charge transfer, the locations measured on the object by the
multiple images are slightly different. This difference depends on
the resolution of the optical system of FIG. 2A, along with other
system parameters.
[0115] FIG. 8A is a simplified schematic illustration of still
another embodiment of a detector 850. The detector 850 is
substantially similar, if not identical, to the detector 750
illustrated and described above in relation to FIG. 7A. In
particular, the detector 850 can again be a chromatic, TDI CCD that
can be used with a fringe projection type autofocus system, e.g.,
the autofocus system 222 (illustrated in FIG. 2A), that is used to
measure the position of a work piece, e.g., a wafer 28 (illustrated
in FIG. 1). Additionally, the detector 850 again includes a
rectangular array of pixels 874 comprising a plurality of rows of
pixels 874R (each row extends from left to right in FIG. 8A, i.e.
in the +Y direction) and a plurality of columns of pixels 874C
(each column extends from top to bottom in FIG. 8A, i.e. in the -X
direction). Further, the detector 850 again includes a plurality of
masks 876 that are fixed relative to the pixels 874 and that extend
over and cover entire columns of pixels 874C. With this design, the
detector 850 includes a plurality of active columns 874AC (i.e.
uncovered or unmasked columns, shown in white), and a plurality of
masked columns 874MC (shown in black). Moreover, in this
embodiment, there are again three masked columns 874MC for every
active column 874AC, which allows up to four different spectral
signals to be collected using a single TDI chip.
[0116] FIG. 8B illustrates the image recorded by active columns of
the detector 850 of FIG. 8A over time. In particular, FIG. 8B shows
the image recorded by those active pixels for times t.sub.0 through
t.sub.3 as the light source 248A (illustrated in FIG. 2A) provides
light 248B (illustrated in FIG. 2A) to illuminate the detector
850.
[0117] Similar to the previous embodiments, the light source 248A
(illustrated in FIG. 2A) is again strobed, such that the wavelength
of the light provided by the light source 248A is selectively
adjusted in discrete increments over time. Stated another way, the
wavelength of the light provided by the light source 248A can be
strobed for times t.sub.0, t.sub.1, t.sub.2, t.sub.3, etc.
Additionally and/or alternatively, other characteristics of the
light 248B generated by the light source 248A can be selectively
adjusted in discrete increments over time. For example, the
polarization and/or other characteristics of the light 248B
generated by the light source 248A can be adjusted in discrete
increments over time.
[0118] In this embodiment, however, only two different spectral
signals are being collected using a single TDI chip. In particular,
as shown in FIG. 8B, at time t.sub.0, the light source 248A
provides light at wavelength .lamda..sub.1 (i.e. .lamda..sub.1 is
on); at time t.sub.1, the light source 248A provides light at
wavelength .lamda..sub.1 (i.e. .lamda..sub.1 is on); at time
t.sub.2, the light source 248A provides light at wavelength
.lamda..sub.3 (i.e. .lamda..sub.3 is on); at time t.sub.3, the
light source 248A provides light at wavelength .lamda..sub.3 (i.e.
.lamda..sub.3 is on); etc. Stated another way, in this embodiment,
only two spectral signals are being utilized (as opposed to the
maximum of four when three masked columns are provided for each
active column, as shown in FIGS. 7A-7C) with each source being left
on for two TDI charge shift cycles.
[0119] Moreover, the rate at which the light source 248A is strobed
can vary depending on the overall capabilities of the system. For
example, in one non-exclusive embodiment, the light source 248A is
strobed at a rate of thirty-four kHz (or 34,000 lines per second),
or half as fast as the example of FIGS. 6 and 7. Alternatively, the
light source 248A can be strobed at a different rate that is
greater than or less than sixty-eight kHz.
[0120] Additionally, for purposes of demonstrating the output of
the present embodiment, FIG. 8B again isolates a single pixel (i.e.
in the X direction) and labels that as Pixel "N" (shown as a dashed
rectangular box).
[0121] In certain embodiments, in order to build a system based on
this TDI mode, the designer must only decide on the maximum number
of independent spectral signals desired, which is determined by the
number of masked columns that are provided with each active column.
The user can always use fewer than the maximum number of
independent spectral signals, such as, for example as illustrated
in FIG. 8B, by simply leaving source one on for two TDI charge
shift cycles, and using source two for two TDI charge shift cycles,
and repeating.
[0122] FIG. 8C illustrates the output signal for a single pixel,
i.e. Pixel "N", of the detector 850 of FIGS. 8A and 8B over time.
In this case, two consecutive data points in time corresponds to
.lamda..sub.1, while the next two consecutive data points then
correspond to .lamda..sub.3. This pattern is then repeated in a
two-two-two-two pattern over time. Assuming the object (in the FP
AF system this is the wafer 28 (illustrated in FIG. 1)) is moving
synchronously to the charge transfer, the result is four repeated
images (2 each of 2 different wavelengths) of nearly the same
locations on the wafer 28 in x and y interleaved in time. The two
repeated images are then combined to accurately determine the
position of the wafer 28. Stated another way, in this embodiment,
the values measured at a particular location from each of the
different wavelengths of light can be combined, e.g., by the
control system 224 (illustrated in FIG. 2A), to accurately
determine the position of the wafer 28. Additionally, it should be
noted that the output signal that is provided from the detector 850
depends on the fringe phase for each wavelength that is provided by
the light source 248A (illustrated in FIG. 2A), with the fringe
phase varying as the position, i.e. the height, of the wafer 28
varies.
[0123] FIG. 9A is a simplified schematic top view (XY plane)
illustration of still yet another embodiment of a detector 950. As
illustrated, the detector 950 is somewhat similar to the detectors
750, 850 illustrated and described above in relation to FIGS. 7A,
8A, respectively. In particular, the detector 950 can again be a
chromatic, TDI CCD that can be used with a fringe projection type
autofocus system that is used to measure the position of a work
piece, e.g., a wafer 28 (illustrated in FIG. 1). Additionally, the
detector 950 again includes a rectangular array of pixels 974
comprising a plurality of rows of pixels 974R (each row extends
from left to right in FIG. 9A, i.e. in the +Y direction) and a
plurality of columns of pixels 974C (each column extends from top
to bottom in FIG. 9A, i.e. in the -X direction). Further, the
detector 950 again includes a plurality of masks 976 that are fixed
relative to the pixels 974 and that extend over and cover entire
columns of pixels 974C. With this design, the detector 950 includes
a plurality of active columns 974AC (i.e. uncovered or unmasked
columns, shown in white)), and a plurality of masked columns 974MC
(shown in black). Moreover, in this embodiment, there are again
three masked columns 974MC for every active column 974AC, which
allows up to four different spectral signals to be collected using
a single TDI chip.
[0124] However, in this embodiment, as illustrated more clearly in
FIGS. 9B and 9C, the detector 950 further includes a lenslet array
978 that is positioned substantially adjacent to a top surface 980
of the array of pixels 974. In particular, FIG. 9B is a simplified
schematic illustration showing fringes of light 246 and a side view
(YZ plane) of the detector 950 of FIG. 9A. Additionally, FIG. 9C is
a simplified schematic illustration showing fringes of light 246
and a side view (XZ plane) of the detector 950 of FIG. 9A.
[0125] In one embodiment, the lenslet array 978 can be a
cylindrical lenslet array. Alternatively, the lenslet array 978 can
have a different design, i.e. can have a different shape. By
placing the lenslet array 978 over the masked top surface 980 of
the detector 950, the lenslet array 978 is able to capture most, if
not all, of the light that would otherwise be blocked or absorbed
by the masked regions, i.e. the masked columns 974MC, on the
detector 950. Moreover, the lenslet array 978 redirects the
captured light to the active regions, i.e. the active columns
974AC, on the detector 950. By way of example, in the embodiment
illustrated in FIGS. 9A-9C, where three-fourths of the pixels 974
are masked, the lenslet array 978 improves the light efficiency of
the detector 950 by up to a factor of four compared to a similar
detector that does not include the lenslet array 978.
[0126] Additionally, as noted above and as shown in FIG. 9C, the
detector 950 can be designed such that the fringes of light 246
that impinge on the detector 950 are at a grazing angle of
incidence 982 of between approximately thirty and eighty degrees
relative to the normal 984 of the detector 950. Moreover, the
grazing angle of incidence 982 can be fixed for a given system
design (i.e the grazing angle of incidence 982 does not vary for a
given fringe projection system). As shown clearly in FIG. 9C, the
grazing angle of incidence 982 is about the Y-axis, such that the
lenslet array 978 will not cause any problems, e.g., shadowing
effects, when used with the detector 950.
[0127] As described in detail herein above, the present embodiment
uses a single TDI CCD detector to obtain signals with different
spectral properties. As a result thereof, multiple CCD chips are
not required, thereby eliminating potential problems that can occur
when multiple CCD chips are used. For example, multiple CCD chips
can be difficult to align, expensive, and can't be used with high
angle off-axis illumination. Further, the present embodiment does
not use color filters built into the CCD, thereby eliminating
additional potential problems that may otherwise exist. For
example, some color filters limit the resolution of the TDI sensor
in the direction perpendicular to the TDI direction by using
columns of chromatic sensors. In addition, if color filters are
built into the CCD, the set of wavelengths that can be
independently measured is determined at the time the CCD is built.
In contrast, the proposed TDI sensor does not have any
predetermined spectral properties other than the full spectral
response of the light sensitive material. Therefore, the spectral
properties of the multiple wavelength signals that are detected can
be changed dynamically by simply changing the light source
properties. The proposed TDI sensor does not limit the spectral
measurements like traditional color CCD sensors in prior art.
[0128] It should be noted that a system including the features of
the present embodiment may be designed to address the issue of thin
film effects (also sometimes referred to as "Goos-Hanchen errors").
Thin film effects involve a shifting of the beam when the beam is
incident on an optical interface, e.g., a substrate that is imaged
by an imaging optical system in the production of a semiconductor
wafer. A proper and necessary approach for compensating for these
thin film effects can include a digital approach and/or an analog
approach. For example, in one such approach, correcting for these
thin film effects for a FP AF system entails signals with different
spectra (i.e. different wavelengths) being collected and compared
to determine the true wafer height. The combination of the
different spectral signals is process dependent. Therefore, the
different spectral signals (which, as shown in the above
embodiments can be two or four different spectral signals, or
another number of spectral signals) sent to the wafer 28 and TDI
CCD detector can change depending on the process. Since the
chromatic TDI CCD detector of the present embodiment, as described
herein, does not include any spectral filters built into the
detector, the desired spectral signals can be set by the
illumination system. A non-exclusive example of a system and method
for compensating for these thin film effects is disclosed in U.S.
patent application Ser. No. 12/884,890, filed on Sep. 17, 2010, and
entitled "GOOS-HANCHEN COMPENSATION IN AUTOFOCUS SYSTEMS". As far
as permitted, the contents of U.S. patent application Ser. No.
12/884,890 are incorporated herein by reference.
[0129] Using a line-scan camera in its natural TDI mode for a FP AF
system, as opposed to the area mode, means a faster, lower noise
system when all other factors are the same. In order to correct for
thin film effects, as discussed above, signals with different
spectral properties must be obtained. As provided herein, this can
be accomplished in a fast, simple, inexpensive way through the use
of a TDI sensor, as such a detector a) does not set the properties
of the spectral bands in the sensor; and b) does not require any
prisms or other complex optical components.
[0130] Additionally, in certain embodiments, two important system
capabilities must be met in order for the autofocus system and the
detector to work effectively as desired. First, the light sources
must be able to turn on/off at least as fast as the maximum line
rate for the TDI sensor. Second, the camera electronics (i.e. the
ADC) must be able to measure signals near the electronic Nyquist
rate, as shown in FIG. 10. The Nyquist rate is the minimum sampling
rate required to avoid aliasing, which can be described as being
equal to twice the highest frequency contained within the signal.
The importance of the two noted system capabilities is due to the
fact that if such system capabilities do not exist, the phase of
the projected fringes from the light source for spectral band 1
(.lamda..sub.1) and spectral band 2 (.lamda..sub.2) could be
completely out of phase. This, in turn, could result in a signal
for Pixel "N" as a function of time that oscillates between the
minimum and maximum electrical values at the line rate. As long as
the necessary electronics can be built into the system to maintain
contrast for this situation, this potential problem can be
effectively avoided.
[0131] In summary, the problem of measuring color images using a
single TDI CCD detector, as is proposed herein, is solved by
masking off parts of the TDI detector chip and synchronizing the
light sources to the charge transfer in such a way that multiple
color images can be captured simultaneously. It should be further
noted that the ability to capture multiple color images
simultaneously is especially useful for the fringe projection type
autofocus system.
[0132] The above embodiments were described as examples of the
projection exposure apparatus of the step-and-scan method, but the
present invention is also applicable to the AF sensor in the
projection exposure apparatus of the step-and-repeat method. The
present invention is further applicable to the AF sensor in liquid
immersion type exposure apparatus, for example, as disclosed in
U.S. Patent Application Publication No. 2011/0086315.
[0133] Furthermore, the above embodiments can also be used in
combination with the AF sensor configured to reduce errors due to
reflecting surfaces as disclosed, for example, in U.S. Patent
Application Publication No. 2009/0116039 and U.S. Pat. No.
8,149,382.
[0134] Further, illumination light is not limited to ArF excimer
laser light (with a wavelength of 193 nm), but can also include
ultraviolet light such as described in, for example, U.S. Pat. No.
7,023,610; a harmonic wave, which is obtained by amplifying a
single-wavelength laser beam in the infrared or visible range
emitted by a DFB semiconductor laser; or a fiber laser with a fiber
amplifier doped with, for example, erbium (or both erbium and
ytterbium), with the wavelength being converted into ultraviolet
light using a nonlinear optical crystal, can also be used as vacuum
ultraviolet light.
[0135] Further, in the embodiment above, a light transmissive type
mask (reticle) is used, which is obtained by forming a
predetermined light-shielding pattern (or a phase pattern or a
light-attenuation pattern) on a light-transmitting substrate, as
disclosed in, for example, U.S. Pat. No. 6,778,257. Alternatively,
an electron mask (which is also called a variable shaped mask, an
active mask or an image generator, and includes, for example, a DMD
(Digital Micromirror Device) that is a type of a non-emission type
image display element (spatial light modulator) or the like) on
which a light-transmitting pattern, a reflection pattern, or an
emission pattern is formed according to electronic data of the
pattern that is to be exposed can also be used. In the case of
using such a variable shaped mask, a stage on which a work piece,
e.g., a wafer, a glass plate or the like, is mounted is scanned
relative to the variable shaped mask, and therefore the equivalent
effect to the embodiment above can be obtained by measuring the
position of this work piece using the position system.
[0136] Further, as disclosed in, for example, PCT International
Publication No. 2001/035168, the embodiment above can also be
applied to an exposure apparatus (a lithography system) in which
line-and-space patterns are formed on wafer by forming interference
fringes on a work piece.
[0137] Moreover, the embodiment above can also be applied to an
exposure apparatus that synthesizes two reticle patterns on a wafer
via a projection optical system and substantially simultaneously
performs double exposure of one shot area on the wafer by one
scanning exposure, as disclosed in, for example, U.S. Pat. No.
6,611,316.
[0138] Incidentally, an object on which a pattern is to be formed
(an object subject to exposure on which an energy beam is
irradiated) in the embodiment above is not limited to a wafer, but
may be another object such as a glass plate, a ceramic substrate, a
film member, or a mask blank.
[0139] The usage of the exposure apparatus is not limited to the
exposure apparatus used for manufacturing semiconductor devices.
For example, the embodiment above can also be widely applied to an
exposure apparatus for manufacturing liquid crystal display
elements in which a liquid crystal display element pattern is
transferred onto a rectangular glass plate, and to an exposure
apparatus for manufacturing organic EL, thin-film magnetic heads,
imaging devices (such as CCDs), micromachines, DNA chips or the
like. Further, the embodiment above can also be applied to an
exposure apparatus that transfers a circuit pattern onto a glass
substrate, a silicon wafer or the like not only when producing
microdevices such as semiconductor devices, but also when producing
a reticle or a mask used in an exposure apparatus such as an
optical exposure apparatus, an EUV exposure apparatus, an X-ray
exposure apparatus, and an electron beam exposure apparatus.
[0140] The surface position detecting apparatus and exposure
apparatus according to the foregoing embodiments are manufactured
by assembling various sub-systems containing their respective
components as set forth in the scope of claims in the present
application, so as to maintain predetermined mechanical accuracy,
electrical accuracy, and optical accuracy. For ensuring these
various accuracies, the following adjustments are carried out
before and after the assembling: adjustment for achieving the
optical accuracy for various optical systems; adjustment for
achieving the mechanical accuracy for various mechanical systems;
and adjustment for achieving the electrical accuracy for various
electrical systems. The assembling steps from the various
sub-systems into the exposure apparatus include mechanical
connections, wire connections of electric circuits, pipe
connections of pneumatic circuits, etc. between the various
sub-systems. It is needless to mention that there are assembling
steps of the individual sub-systems, before the assembling steps
from the various sub-systems into the exposure apparatus. After
completion of the assembling steps from the various sub-systems
into the exposure apparatus, overall adjustment is carried out to
ensure various accuracies of the entire exposure apparatus. The
manufacture of the exposure apparatus is desirably performed in a
clean room in which the temperature, cleanliness, etc. are
controlled.
[0141] Incidentally, the disclosures of all publications, the PCT
International Publications, the U.S. patent application
Publications and the U.S. patents that are cited in the description
so far related to exposure apparatuses and the like are each
incorporated herein by reference.
[0142] Semiconductor devices can be fabricated using the above
described systems, by the process shown generally in FIG. 11A. In
step 1101, the device's function and performance characteristics
are designed. Next, in step 1102, a mask (reticle) having a pattern
is designed according to the previous designing step, and in a
parallel step 1103, a wafer is made from a silicon material. In
step 1104, the mask pattern designed in step 1102 is exposed onto
the wafer from step 1103 by a photolithography system described
hereinabove in accordance with the present embodiment. In step
1105, the semiconductor device is assembled (including the dicing
process, bonding process and packaging process). Finally, the
device is then inspected in step 1106.
[0143] FIG. 11B illustrates a detailed flowchart example of the
above-mentioned step 1104 in the case of fabricating semiconductor
devices. In FIG. 11B, in step 1111 (oxidation step), the wafer
surface is oxidized. In step 1112 (CVD step), an insulation film is
formed on the wafer surface. In step 1113 (electrode formation
step), electrodes are formed on the wafer by vapor deposition. In
step 1114 (ion implantation step), ions are implanted in the wafer.
The above mentioned steps 1111-1114 form the preprocessing steps
for wafers during wafer processing, and selection is made at each
step according to processing requirements.
[0144] At each stage of wafer processing, when the above-mentioned
preprocessing steps have been completed, the following
post-processing steps are implemented. During post-processing,
first, in step 1115 (photoresist formation step), photoresist is
applied to a wafer. Next, in step 1116 (exposure step), the
above-mentioned exposure device is used to transfer the circuit
pattern of a mask (reticle) to a wafer. Then in step 1117
(developing step), the exposed wafer is developed, and in step 1118
(etching step), parts other than residual photoresist (exposed
material surface) are removed by etching. In step 1119 (photoresist
removal step), unnecessary photoresist remaining after etching is
removed. Multiple circuit patterns are formed by repetition of
these preprocessing and post-processing steps.
[0145] While a number of exemplary aspects and embodiments of a
position system 22 and an autofocus system 22A have been discussed
above, those of skill in the art will recognize certain
modifications, permutations, additions and sub-combinations
thereof. It is therefore intended that the following appended
claims and claims hereafter introduced are interpreted to include
all such modifications, permutations, additions and
sub-combinations as are within their true spirit and scope.
* * * * *